The present invention relates to the measurement of the relative densities of produce.
Commercial sorting of fruits and vegetables (hereafter referred to as “produce”) often utilizes density measurement (the weight of the produce divided by the volume of the produce) as a way of discriminating between produce that is ripe and produce that is not ripe. This is because ripe produce has higher density than unripe produce.
For example, grapes are floated in tubs of saltwater with a predetermined specific gravity. Those grapes with high enough density to be considered ripe and sweet will just sink in the saltwater, while those grapes of insufficient density to be considered ripe and sweet will float in the saltwater. The grapes that float pass over and the grapes that sink are collected.
Similarly, pieces of produce such as oranges or peaches are each weighed, and the volume of each piece is measured; the quotient density is used to separate or grade the produce not only by size but also by ripeness. Thus the produce is sold in segregated groups by size and density.
However, after the produce has been so sorted, or if it has not been sorted at all, it often sits in warehouses, or on the store shelves, where it is subjected to variations in temperature and humidity such that the ripeness and desirability of the produce may change over time. The ultimate consumer of the produce wants to be able to ascertain whether or not the produce has desirable density and therefore ripeness or juiciness. In other words, the consumer wants to be able to tell if the orange or other produce being purchased is juicy and sweet or dried out and/or mealy in texture.
It is possible in the prior art to measure the density of produce by weighing the individual piece and measuring the individual volume, then dividing the weight by the volume to obtain the density. Comparing this value to an average, or expected value of density for that particular produce at conditions of ripeness or juiciness provides a discriminator of ripeness or juiciness for the individual piece in question.
Unfortunately, while it is fairly simple to measure the weight of a piece of produce, it is difficult to measure the volume because the shape of the produce is usually irregular and non-spherical. This makes it difficult to approximate volume by assuming that produce geometry matches known and easily calculated volumes of familiar geometric shapes, specifically spheres.
Because of the irregular geometry, the most commonly used method for measuring volume is to measure the volume of a liquid displaced by the volume of the produce. The volume of liquid displaced is measured in volumetrically graded containers and the volume of the produce is imputed from the volume of liquid displaced. Thus in order to measure density, the produce must be placed in a liquid bath.
Another method of measuring produce volume is by making numerous and precise measurements of the dimensions of the produce and computing, by many possible algorithms known in the art, the actual volume.
Yet another method is to place the produce in a chamber of known shape and volume (such chambers are often referred to as Helmholtz resonators) and to measure the difference in the resonance of the volume of air in the cavity with and without the produce. The resonance is a function of volume, and known algorithms are used to compute the volume of the produce.
Each of the foregoing methods, has a level of cost and difficulty which makes it undesirable as a quick means of ascertaining liquid content per unit volume of the produce, also called, and hereinafter referred to as relative density or “juiciness”. A consumer standing in a supermarket or other venue, confronted with a bin full of produce, might like to have a simple, non-destructive, fast and sufficient means at his or her disposal for determining if the piece of produce in hand, that looks, feels, smells and otherwise seems acceptable, is also juicy. The present invention is intended to address the difficulties and shortcomings of prior methods and to provide a low-cost, simple, non-damaging, fast and sufficient means of ascertaining the relative liquid content of pieces of produce.
Produce of a single species is substantially similar in shape regardless of size. This enables comparative ranking of produce density because the errors of measurement of weight and particularly volume are constant multiples of the actual volume and weight. Any ranking of densities containing such errors in constituent weight or volume will still yield a correct ranking of density, even though the absolute measurement of density in engineering units will be incorrect. This constitutes an important advantage of the present invention.